In a conventional optical fiber sheet, optical fibers are disposed between two flexible resin sheets having the same size as each other which are attached together. Such a conventional optical fiber sheet is usually manufactured by disposing optical fibers on surfaces of sheets on which a pressure sensitive bonding agent (adhesive agent) is applied, and attaching a sheet on which a pressure sensitive bonding agent is applied thereto. Optical fiber sheet is used mainly for a wiring section in an optical fiber in an optical apparatus.
For example, in case in which an extra length part of the optical fiber path is disposed for an optical fiber sheet, it is limited to bend the optical fiber. If such an extra length pat to be used for a wiring section is too long, the optical fiber wiring section is too dense (crowded); thus, there occur direct crosses between the optical fibers in the sheet too often. Therefore, such a direct cross region becomes a bulge; thus, there is a disadvantage in that it is difficult to fix the disposed optical fiber. That is, if so many optical fibers crosses each other, close contact (adhesion) in both sheets which are disposed vertically tend to be reduced; thus, it may occur that the disposed optical fibers move undesirably. When the optical fiber is not fixed in a desirable position in the sheet reliably, the optical fibers cannot be disposed in the sheet accurately so as to be assembled in a device due to its successive usage for a long period. In some cases, there is a concern that the optical fiber may be damaged.
Also, a multiple crossings may occur easily in which a plurality of optical fibers crosses each other collectively. In such a multiple crossing region, there is a concern that an unacceptable bending may occur on the optical fibers. Furthermore, there is a case in which a sheet area must be enlarged so as to prevent the multiple crossings.
Also, in the above conventional optical fiber sheet, when an optical connector is attached to the optical fiber which expands from the sheet near an marginal end of the optical sheet, it is not possible to attach the optical connector if the optical fiber which is expanded from the marginal end of the sheet is too short. Therefore, predetermined extra length of the optical fiber is necessary so as to attach the optical connector near the marginal end of the sheet. Also, for a case in which the optical connector is failed to be attached, it is necessary to prepare a greater extra length of the optical fiber so as to cut the optical fiber to attach the optical fiber again. Therefore, it is necessary to prepare a predetermined length of optical fiber from a marginal end of the sheet to a rear end of the optical connector. Thus, there is a disadvantage in that it is difficult, or impossible, to manufacture an optical fiber sheet if the optical fiber has a short extra length, or if the optical fiber has no extra length.
Also, in an optical fiber sheet, a plurality of optical fibers are usually disposed. That is, only an optical fiber is not disposed in an optical fiber sheet. When optical connectors are attached to a plurality of optical fibers respectively near the marginal end of the sheet such that a distance from the marginal end of the sheet should be constant, it is necessary to adjust the length of the extra portion of the optical fiber so as to realize a low skew (that is, to reduce non-uniform distances from the marginal end of the sheet). In the above conventional structure, it is necessary to prepare an area in the optical fiber sheet for disposing an extra length of the optical fiber so as to adjust the extra length of the optical fiber in addition to a necessary area for disposing an optical fiber. Therefore, size of the optical fiber sheet may becomes undesirably large.
Here, in case in which a lot of optical fibers are disposed such that the extra length of optical fiber is disposed in the same area as the necessary wiring area, the wiring condition of the optical fibers become more complicated; thus, a multiple crossing in which more than three optical fibers cross each other collectively may occur easily. Furthermore, the optical fibers may be bent in an area in which the optical fibers are crossing each other. If two optical fibers are crossing, the bending of the optical fibers may be acceptable. However, if more than three optical fibers are crossing, the bending of the optical fibers may not be in an acceptable range. Furthermore, there is a bulge of the optical fibers in such a crossing area; thus, there is a concern that the adhesion of the sheet may be insufficient.
In order to solve the above problems, it is necessary to form an area for disposing an extra length of the optical fiber in addition to a necessary area for disposing the optical fiber by enlarging the sheet area.
Such an area for disposing an extra length of the optical fiber is not limited in a case for attaching the optical connector. That is, such an area for disposing an extra length of the optical fiber is necessary in various cases in which extra length of the optical fiber is needed.